1. Field of the Invention
The present invention relates to a magnetic recording medium having excellent running durability, and more particularly to such a magnetic recording medium which contains ethylene trifluoride chloride and a fatty acid ester.
2. Description of the Prior Art
In magnetic recording media obtained by coating a mixture of a magnetic powder or particulate matter and a binder on a polyester film, the expansion of uses thereof has imposed the requirement of even higher performance on them. For example, in the recent cassette tapes for audio components, video tapes etc., those having more excellent frequency characteristics have been required, and to comply with such a requirement, it has been contemplated to uniformly disperse magnetic particles in a magnetic layer, that is, impart good dispersibility, to enhance the surface properties of the magnetic layer to reduce spacing loss, further to impart appropriate softness to improve the touch with a head, and so forth. However, such a direction is rather disadvantageous in view of running durability, because it tends to increase friction.
On the other hand, the use conditions have become more and more severe because users have been widely spread all over tha world, and therefore the requirement on the durability has become even more severe than ever. The present inventors have been continuously studying on these mutual problems and, as a result, have discovered that the inclusion of ethylene trifluoride chloride and a fatty acid ester in a magnetic layer can reduce friction and hence enhance durability. More specifically, although there have heretofore been known such lubricants as higher fatty acids, silicone oils, ethylene trifluoride chloride (fluorine oil), sorbitan fatty acid esters etc., even these lubricants could not provide a magnetic recording medium having excellent frequency chacteristics as described above.
According to this invention, it has been found that by including an ethylene trifluoride chloride polymer of a low degree of polymerization and a fatty acid ester in a magnetic layer at the same time, a synergistic effect in lubrication is obtained, thereby friction is satisfactorily reduced and durability is improved.